1. Field of the Invention
The invention relates to power operated retractable stop assemblies.
2. Background Art
The use of industrial retractable stop products has become wide spread, due at least in part to high demands in the automotive and heavy equipment industries. Conventionally, a retractable stop is powered by a linear actuator such as an air or hydraulic cylinder, a solenoid actuator, or a rotary actuator with a linear worm gear.
A power operated retractable stop assembly typically includes a reciprocatable rod member driven by the linear actuator, and an assembly body secured to the driving cylinder. Some of these existing assemblies, such as those described in U.S. Pat. No. 4,184,579, utilize a stop lever for stopping and releasing loads traveling on a conveyor. In such an assembly, a blocker leg is used to prevent pivoting of the stop arm causing an uncushioned hard stop of loads traveling on the conveyor when the blocker leg is in the blocking position.
Other existing assemblies attempt to provide a cushioned stop by using cylinder pressure to hold the stop arm in the blocking position. However, assemblies such as these may be disadvantageous in that there is no guarantee of a stop, and a heavy load may deflect the stop lever against the biasing cylinder pressure and continue right past the retractable stop without stopping. Sometimes, assemblies utilize a first mechanism for actuating and deactuating the stop and utilize a separate shock absorber mechanism, such as the assembly described in U.S. Pat. No. 5,168,976.
Other existing assemblies use a linear actuator rod interfering at a right angle with the direction of travel of the conveyor load. This has the disadvantage of side loading the actuator which is designed for the loads to be in line with the center line of the actuator. This creates excessive wear of the actuator. Also, excessive side load on a linear actuator can cause the actuator to bind and be unable to release without first releasing the load.
Although the existing retractable stop assemblies that provide a hard stop and those assemblies that attempt to provide a cushioned stop by using cylinder pressure have been used in many applications that have been commercially successful, these assemblies have disadvantages. In some applications, it may be desirable to provide a cushioned stop, and assemblies providing a hard stop without any cushion may not be desired. Further, although a cushion may be desirable in some applications, because assemblies providing a cushioned stop cannot guarantee a stopping of the load after the cushion, these assemblies may also not be desired. Further, assemblies utilizing a separate shock absorber mechanism are complex and costly, so these assemblies may also not be desired.
Power operated retractable stop assemblies with integral cushion and stopping mechanisms are described in U.S. Pat. No. 6,119,843. These power operated retractable stop assemblies provide a cushion when stopping a load and provide a hard stop at the end of the cushion zone. These existing retractable stop assemblies that provide integral cushion and stopping mechanisms have also been used in applications that have been commercially successful.
There is an opportunity for improvement in integral cushion and stopping mechanisms in the situation where the stop arm remains near the locked position after the drive arm, which drives the stop arm, is driven to the unlocked position. That is, the stop arm balances near the locked position even though it has been released by the drive arm. If this situation occurs in a conveyor arrangement where there is cross-traffic, and the stop assembly is located at a cross-traffic point, the balanced stop arm may interfere with the cross-traffic.
The balanced stop arm condition also makes it difficult for a worker to determine the position of the drive arm and the driving cylinder by visual inspection. When the worker sees the stop arm at the locked position, the worker may assume that the cylinder has been actuated to cause the drive arm to engage and drive the stop arm. However, this assumption is not correct in the case where the stop arm balances near the locked position after it has been released by the drive arm.
Another opportunity for improvement in integral cushion and stopping mechanisms occurs when the retractable stop assembly is mounted in an inverted orientation. Because the assembly is in an inverted orientation, the stop arm may again balance near the locked position after the drive arm is driven to the unlocked position. Even if the stop arm has been pushed to the open position by a passing load, gravity will cause it to return to the locked position. That is, the stop arm hangs near the locked position even though it has been released.
Although the existing power operated retractable stop assemblies with integral cushion and stopping mechanisms have advantages, there are still situations where these assemblies may have shortcomings. In particular, the potential for a balanced stop arm condition may make it undesirable to use these assemblies in certain conveyor applications and in certain applications requiring the assemblies to be mounted in inverted orientations.
For the foregoing reasons, there is a need for an improved power operated retractable stop assembly.